Reverberation method and system



June 3, 1947 B. vKREUzr-:R

REVERBERATION METHOD AND SYSTEM Filed Feb` 8, 1945 @N MHQN NSK@ SQQPatented June 3, 1947 UNITED REVERBERATION METHOD AND SYSTEM BartonKreuzer, Philadelphia, Pa., assignor to Radio Corporation of America, acorporation of Delaware Application February 8, 1945, Serial No. 576,812

Claims.

This invention relates to sound recording methods and systems, andparticularly to a sound rerecording system wherein the original soundrecord is modied with respect to amplitude or frequency, or both.

It is Well-known that sound records, especially those which accompanymotion pictures are generally rerecorded, while records made for radiobroadcasts or home reproduction in phonographs may also be rerecordedbefore release. In motion picture work, rerecording is employed tocombine dialogue, background effects, and/or music into a compositerecord for the picture, the various components being modified eitherwith respect to amplitude or frequency, or both. Amplitude and frequencymodiiications are also made during the rerocording of a singleprerecorded record, particularly to simulate the sound as it would occurat the place of the scene. The sound may be recorded in a studio or on aset, which is actually only a portion of the entire scene, and thus, thequality of the sound is not appropriate to the scene being depicted inthe picture. For instance, only two or three sides of a large hall orcave may be used, and the sound detected from the actors therein doesnot have the characteristic it would have had if produced in the actualhall or cave. However, by rerecording, the sound may be characterized byvarying the amplitude and frequency relationship of its components, andby introducing reverberation, to give it the quality it would have hadif actually recorded at the scene of action.

As disclosed in my copending application, Ser. No. 576,811, filed Feb.8, 1945, reverberation is also used to improve or restore noisy records.In accomplishing sound wave modification, reverberation chambers areemployed, and have been ernployed for some time. Reverberation chambersare simply enclosed spaces into which sound is projected by a speakerand detected by a microphone spacially disposed with respect to thespeaker. To simulate large halls, railroad stations, caves, and thelike, it is desirable to have a reverberation chamber of large size inorder to get a true and accurate sound modification to simulate thescene, and such space is usually not readily available. The presentinvention is directed to a system which permits the use of the unusedspaces in a studio or building not otherwise suitable for this purpose,such as a basement area, the plenum space in a building, or the actualrecording stage itself While in use. Reverberation may, of course, beadded to and during the original recording from a recording stage, thepresent invention permitting the stage to be used simultaneously forboth the original sound source and the reverberation chamber.

One of the important features of the invention is the use of an ultra orsupersonic frequency, which, of course, is not only inaudible to theperformers, but also is inaudible to the audio detecting elements ormicrophones. Since the ultrasonic carrier modulated by an audio signaloccupies only a relatively narrow band in its spectrum, a very highquality result is obtainable, while the use of an ultrasonic frequencyas a carrier permits the reverberation chambers to be tanks or pipesfilled with a liquid,

The principal object of the invention, therefore, is to facilitate themodification of a sound wave as recorded.

Another object of the invention is to provide an improved method of andsystem for obtaining reverberation in a signal being transmitted orrecorded.

A further object of the invention is to provide an improved method ofreverberating an audio signal.

A further object of the invention is to obtain reverberation in spacenot normally suitable therefor.

A still further object of the invention is to obtain reverberation of anaudio signal by modulating an ultrasonic signal, which is reverberatedand thereafter detected to obtain a reverberated audio signal.

Although the novel features which are believed to -be characteristic ofthis invention Will be pointed out with particularity in the appendedclaims, the manner of its organization and the mode of its operationwill be better Vunderstood by referring to the following descriptionread in conjunction with the accompanying drawings forming a parthereof, in which the single figure is a diagrammatic arrangement of arecording or rerecording sytem embodying the invention.

Referring now to the drawing, a source of signal currents to bereverberated is shown at 5 as a reproducer, which may be either film ordisc, although it is to be understood that this source could be amicrophone directly detecting the original sound source or sources. Theoutput of the reproducer is fed into an amplier 6, the output of whichis divided, one portion going to an amplifier 8 feeding a recorder iland a monitoring speaker l2 through a mixer 9. This channel contains theessential elements of a normal recording system, the mixer operatorvarying the amplitude of the currents in the proper amounts within thelimits of the recorder II.

The othe1` portion of the output from the amplier 6 is fed into amodulator I5 which is supplied with an ultrasonic carrier frequency,such as 30,000 cycles, from a generator I6, the output of the modulatorbeing fed to an ultrasonic reproducing speaker I8 in a reverberationchamber 20. The ultrasonic frequency sidebands produced by modulationare reverberated in the chamber 20 and picked up by an ultrasonicmicrophone 2 I, amplilied in amplier 22, and detected in a demodulator24 to obtain the original audio frequencies. rihe reverberated audiosignal is then ampliiied in amplifier 25, impressed on a mixer 26, andthen on the recorder II and monitor I2. By the proper adjustments of themixers 9 and 26, as indicated in the monitor I2, the normal andreverberated currents are mixed together in the desired proportions forrecording into the final record.

Although a split channel has been illustrated wherein only a portion ofthe signal is reverberated, it will be understood that the entire signalmay be passed through the reverberation chamber or the operator may useonly that portion passing through the reverberation chamber. Alsoy sincethe ultrasonic frequency spectrum is very large compared with the audiofrequency range which determines the Widths of the sidebands (one ofwhich may be suppressed), it is feasible to utilize the reverberationchamber for reverberating more than one audio signal simultaneously.That is, by the use of a second reproducer, shown at 30, and anotherdetector, shown at 3I, two or more audio signals could be reverberatedsimultaneously by using a different carrier frequency for each audiosignal. Furthermore, the same ultrasonic wave translator and detectorcould be used for a plurality of carriers, the carriers being separatedby electrical band pass lters, as is well-known in the art.

As mentioned above, the unused spaces of a building may now serve asreverberation chambers, such as the basement or attic, or the actualrecording stage during the original sound Droduction. In the latterinstance, the audio frequency elements are insensitive to the ultrasonicfrequencies, and the ultrasonic elements are not sensitive to the audiofrequencies, so there is no interference therebetween. Also, since therange of the ultrasonic reproducer and detector is large and only a Verynarrow range is employed, a uniform response is obtained.

By the use of ultrasonic frequencies as the reverberation medium, tanksor pipes lled with liquid can be used with under water sound propagatorsand detectors. By varying the tuning of the carrier generator, variousreverberation characteristics are obtainable, thus avoiding changing thesize of the chamber as is now necessary with audio frequency chambers.The system thus is particularly flexible to provide a wide range ofsound characteristics covering spaces having a wide range in size, whilepermitting the same chamber to be used for reverberating several signalssimultaneously.

I claim as my invention:

l. A reverberation system comprising a plurality of generators of superaudible electrical currents, each current having a different frequency,a plurality of signals in the audio spectrurn, a reverberation chamber,means for modulating each of said super audible currents with arespective audio signal, means for simultaneously generating ultrasonicwaves from said products of modulation Within said chamber, means fortranslating said reverberated Waves into corre sponding electricalcurrents, and a demodulator for each of said electrical currents ofdifferent frequency,

2. The method of generating and detecting a signal in a certain area andsimultaneously regenerating and again detecting said signal in said areacomprising detecting sound waves from the original source of said Wavesin a certain area, modulating a supersonic carrier frequency with theproducts of detection, reproducing the products of modulation in saidcertain area, and detecting said reproduced products of modulation.

3. The method in accordance with claim 2, in which said detectedproducts of modulation are combined with said origina-l products ofdetection.

4. A method of producing artiiicial reverberations on a sound stagewithout interfering with the normal recording operations being conductedthereon comprising producing an audible sound signal on said stage,detecting said signal during the production thereof, generating asuper-audible carrier frequency, modulating said carrier with saiddetected signal, translating said products of modulation into ultrasonicwaves Within the space of said sound stage, detecting said ultrasonicwaves within said space, and demodulating said detected currents toobtain a reverberated original signal.

5. The method of obtaining varying reverberation characteristics of anaudio signal without modifying the reverberation chamber, itself,comprising generating a super-audible carrier of predeterminedfrequency, varying the frequency of said carrier to obtain desiredchanges in reverberation characteristics, modulating said carrier withsaid audible signal, generating ultrasonic waves with the products ofmodulation, reverberating said waves, translating said waves intoelectrical currents, and demodulating said last mentioned currents.

BARTON KREUZER REFERENCES CITED rThe following references are of recordin the le of this patent:

UNITED STATES PATENTS Number Name Date 2,318,417 Phelps May 4, 19431,853,286 Round Apr. 12, 1932

